Battery/Ultracapacitor (UC) Hybrid Energy Storage Systems (HESS) for Electric Vehicles have been previously proposed in the literature to increase battery cycle life. The HESS consists of a Power Management Strategy and an Energy Management Strategy.
In this work, an improved HESS management strategy is proposed, involving a more comprehensive method of setting the UC energy level using a speed-dependent band, where worst case scenarios and real-life drive cycles are considered. This allows the UC to achieve two goals – to contain sufficient energy for future accelerations, and have sufficient space for energy from future regenerative braking – without prior route knowledge.
Simulations of the proposed strategy show the goals being achieved, and battery cycle life has indeed been extended. Also, existing works are shown to be unable to achieve the goals simultaneously unless their UCs are sized larger. Lastly, a reduced-scale experiment was built to prove the proposed strategy is physically feasible.